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Full text of "Text Book Of Mechanical Engineering"

Appendix  VL

1187

The Sims-Bosch magneto ignition has been described on
p. 965. Objection to low-tension failures in some gases on
the one hand, and short circuiting by high-tension arrange-
ments, resulted in the introduction of the Eisemann system,
Fig. 1043, where an intermediate tension alternating current is
generated by the armature N within the magnet A, and taken off
by slip rings G to the primary circuit M, an interrupting cam B
breaking the circuit at H. The coil c is without trembler, for the
current is already alternating, and transforms the primary into the
secondary current in line P, which is connected to the distri-
butor j, whence it is taken to the firing plugs E by L L and returned
by earth D. The rest will be understood from Fig. 1044.

Governors are now fitted to car engines, and, instead of letting
them close the exhaust valve as formerly, they usually act on a
throttle valve to adjust the supply of mixture without altering its
proportions, producing a very sensitive regulation at all speeds.
The Murray governor, Fig. 1045, *s an example. The governor
shaft is driven from the engine, and, as the balls fly out with
increased speed, they act upon a lever B, which relieves a spring-
loaded throttle valve E, and the supply of mixture is reduced.
The wedge M, however, intervenes to an extent decided upon by
the hand lever L, so the governor action becomes early or late,
and is therefore compelled to hold up the car at any standard
speed desired by the driver.

The starting of the engine is effected by the handle F,
Fig. 1046, which is pressed against the spring G till the ratchets K
and j engage, and thus rotate the engine shaft H. To do this
easily the compression may be prevented for the first stroke or
two by opening the exhaust valve, and closing it again when the
explosions commence, though multiple-cylinder engines will start
easily without this precaution. The ratchets are released by the
spring when the pressure is removed.

To reduce the exhaust noise the gaseous stream must be split
into fine jets, while providing sufficient area to avoid undue back
pressure, The Stanley Silencer, Fig, 1047, does this satisfactorily.
Exhaust gases enter at A and pass through fine holes c D E F on
their way to the outer air, being further split up by baffle pins
within the pipes-